Multifilament sutures are generally made by braiding yarns into a braided structure. Appropriate braided constructions for surgical sutures have been described in U.S. Pat. Nos. 5,019,093; 4,959,069 and 5,059,213 (all incorporated by reference herein). After the braided construction has been made the braid is cleaned by scouring and generally compacted by hot stretching the braid multifilament.
One suitable means for hot stretching braided constructions is illustrated in FIG. 1. A spool of braided multifilament is attached to a tensioning device. The braided multifilament is then wound around feed rolls (4 and 6 respectively) and threaded through heated plates 8. The braided multifilament is then drawn by draw rolls 10 and 12 and collected on take up spool 14. The drawing is accomplished by rotating the draw rolls faster than the feed rolls to stretch the braided multifilament. Generally the braided multifilament are drawn in the range of from about 10 to about 20 percent. The amount that the suture is to be drawn depends on the size of the suture, the material the suture is made of and the braid construction. Similarly the temperature and residence time for the braided multifilament would have between the heated plates would also depend on these same factors.
Unfortunately, this process and apparatus although effective in providing a hot stretched braided suture resulted in two potential defects being introduced into the braided multifilament sutures. The first defect is slight increase in the number of sutures that do not pass quality assurance strength tests. The second defect is a tendency for the braid to have irregular bunching in the braid.
Therefore, it is an object of the present invention to provide a method and apparatus for hot stretching braided multifilament sutures that results in little or no strength loss associated with hot stretching. Alternatively, it is an object of the present invention to provide an apparatus and process for hot stretching braided multifilament sutures which reduces or eliminates bunching in braided multifilament sutures.